Resumen de Advanced characterization and modelling of charge transfer in perovskite solar cells
This thesis includes the work done in ICIQ about fabrication, characterization, and modelling of hybrid perovskite solar cells.
Coming from other kind of solar cells, the analysis tools, the methods, and, most importantly, their interpretation have been analysed and adapted to this new kind of device.
Then, these techniques has been employed for analysing and understanding the influence of four different and novel hole transport materials on perovskite solar cells voltage.
Another study focussed on the electrons accumulation in devices employing small variations in each stacked layer thickness and analysing the samples using the same techniques.
From by international stay in Dr. Piers Barnes and Prof. Jenny Nelson groups in Imperial College London another study was originated exploring the complex interpretation of impedance spectroscopy results when applied on perovskite solar cells with mobile ions.
Finally, all the free software that has been developed for data acquisition and processing and for drift-diffusion modelling of perovskite solar cells have been exposed.
The objectives of this thesis are: 1. synthesize different kinds of lead perovskite absorbers (e.g. MAPbICl,MAPbI3, FAMAPbIBr, CsFAMAPbIBr); 2. fabricate solar cells with different structures (e.g. top and bottom cathode); 3. test different materials for selective contacts, either known (e.g. flat or mesoporous titania, PCBM or plain fullerene) or novel materials obtained via collaborations (e.g. TAE-1, TAE-3, TAE-4); 4. optimisation of the devices fabrication in order to get close to the state of the art devices; 5. characterisation of the prepared devices using the existing routinely techniques (e.g. current-voltage sweeps); 6. characterisation using advanced small perturbation techniques; 7. optimisation of the characterisation methods, data acquisition, and data processing; 8. obtain information on the charge accumulation and charge dynamics from the characterisation output; 9. model perovskite solar cells and compare the expected theoretical output with the experimental one; 10. where the simulation matches the experiment, take advantage of the additional insight obtainable from the modelling.
The contents of this thesis are: In chapter 1, an overview on the solar cells main concepts and working mechanisms are presented.
Perovskite solar cells are inserted in the provided framework and the research state of the art is briefly described.
In chapter 2, materials, equipment, and fabrication of the studied perovskite solar cells are described in detail.
In chapter 3, followed conventions, routinely and advanced characterisation techniques are described.
For each characterisation technique the involved concepts, formalism, and equations required for the data analysis are explained.
Additionally, I presented here my own observations and thoughts about the interpretations of the characterisation output, presenting also unpublished results from drift-diffusion modelling.
In chapter 4, the performances of bottom cathode perovskite solar cells fabricated using four different hole transporting materials are compared.
Then the origin of the observed differences are studied by means of small perturbation transient techniques.
Part of this chapter has been published in I. Gelmetti, N. F. Montcada, A. Pérez-Rodríguez, E. Barrena, C. Ocal, I. García-Benito, A. Molina-Ontoria, N. Martín, A. Vidal-Ferran and E. Palomares, Energy Environ. Sci., 2019, 12, 1309–1316. DOI: 10.1039/C9EE00528E In chapter 5, top cathode solar cells have been fabricated exploring the thickness of each layer.
For each device, the advanced characterisation output have been compared obtaining insight on the charge storage location.
Part of this chapter has been published in I. Gelmetti, L. Cabau, N. F. Montcada and E. Palomares, ACS Appl. Mater. Interfaces, 2017, 9, 21599–21605. DOI: 10.1021/acsami.7b06638 In chapter 6, drift-diffusion modelling of perovskite solar cells is employed for understanding the features observed in impedance spectroscopy.
Specifically, the implemented simulation is described and the resulting apparent capacitance at different illumination, bias, and frequency is explained.
Part of this chapter has been published in D. Moia, I. Gelmetti, P. Calado, W. Fisher, M. Stringer, O. Game, Y. Hu, P. Docampo, D. Lidzey, E. Palomares, J. Nelson and P. R. F. Barnes, Energy Environ. Sci., 2019, 12, 1296–1308. DOI: 10.1039/C8EE02362J In chapter 7, various software I implemented during my thesis is described.
First, the implementation of more functions and simulations for drift-diffusion modelling is shown.
Second, the development of a graphical user interface for current-voltage sweeps acquisition is presented.
Third, the scripts used for automated and reliable data analysis are reported; they have been used for plotting most of the graphics included in this thesis.
